In the prior art, referring to FIG. 1 and FIG. 2, a secondary battery comprises a cap plate 1, at least two cells 2 and two connecting pieces 3. Each connecting piece 3 has: a tab electrical connecting portion 31 for electrically connecting with a corresponding tab 21 of each cell 2 (such as via welding); an electrode terminal electrical connecting portion 32 connected to the tab electrical connecting portion 31 along a longitudinal direction (referring to FIG. 1 and FIG. 2, the longitudinal direction is parallel to a lengthwise direction L) of the connecting piece 3 for electrically connecting with a corresponding electrode terminal 11 of the cap plate 1 (such as via welding); and a transition portion 35 positioned between the tab electrical connecting portion 31 and the electrode terminal electrical connecting portion 32 and electrically connecting the tab electrical connecting portion 31 and the electrode terminal electrical connecting portion 32. In the secondary battery, in case of thermal runaway of the cell 2, generally, the transition portion 35 between the tab electrical connecting portion 31 and the electrode terminal electrical connecting portion 32 is firstly fused, then the cell 2 and the electrode terminals 11 are electrically disconnected, therefore an electrical circuit between the cell 2 and the electrode terminal 11 are disconnected, however, an electrical connection between the cell 2 and other cell(s) 2 which are electrically connected in parallel cannot be disconnected. For example, when an internal short circuit in one cell 2 occurs first, the one cell 2 will be reversely charged by the other cell(s) 2, a short-circuit current of the one cell 2 becomes larger, more heat is generated and temperature rise increases, therefore the thermal runaway more easily occurs in the one cell 2.